This invention relates to scraper apparatus for settling basins, such as sludge traps and the like having a bridge transportable above the basin, a scraper blade mounted for upward pivotal movement thereon by a pivot arm and a loading device which generates a return force that moves the scraper blade toward the scraping position.
Scraper apparatus of the above mentioned type is disclosed in German patent No. 1 179 160. The scraper disclosed in this patent has a pivot arm which extends vertically. This is particularly advantageous, where longitudinal scrapers are employed because the scraper blade can then actually be transported up to the end of the basin, which is not possible with scraper blades, which are trailed from the bridge at an angle. However, with the pivot arm in this vertical position, the return moment generated by the deadweight of the scraper blade is substantially zero, so that the scraper blade does not exert an adequate scraping force and would escape rearwardly by a small scraping resistance. It is for this reason that a loading device is provided which ensures the exertion of an adequate return force and scraping force even in the vertical position of the scraper blade. In prior art apparatus the loading device embodies a loading weight mounted pivotally on a lever arm on the bridge, with the bridge being connected to the pivot arm of the scraper blade through the intermediary of a knee lever which is bent during upward pivotal movement of the scraper blade and is extended or spread during the descent of the scraper blade. This arrangement has the advantage in that during the upward pivotal movement of the scraper blade the stroke distance of the loading weight is considerably shorter than that of the scraper blade.
A disadvantage of such prior art apparatus is that the return force exerted by the loading device decreases greatly even at the beginning of the pivotal movement of the scraper blade. If the scraper blade is forced by a thick and compact accumulation of sludge to escape or move out of the vertical position against the maximum return force exerted by the loading device, then the return force of the loading device decreases so rapidly that the scraper blade is even incapable of scraping away only the top layer of the sludge accumulation. This is true even though the pivot arm and scraper blade, in escaping or moving rearwardly, generate a return force by their deadweight which acts on a lever arm. That is, such force is far from being sufficient to compensate for the reduction in the return force of the loading device.